This invention relates to wireless communication systems in which areas served by the wireless communication system are divided at least into cells, and more particularly, to a system for dynamically allocating available system channels to wireless terminals requiring service.
A problem in the art of wireless communication is to minimize interference between the links, each of which uses at least one channel, employed in neighboring cells while maximizing the overall use of the available spectrum. One prior art method to increase the spectrum utilization is to reuse the same channels at appropriate geographic separations. How to arrange the assignments of the channels to cells so that they may be reused to maximize the overall use of the available spectrum while minimizing the interference between the channels is the so-called xe2x80x9cchannel reuse problemxe2x80x9d.
It has been recognized in the art that dynamic channel assignment systems perform better than static channel assignment systems. One reason for this is because the number of users in any particular cell changes over rime, and such dynamic systems can respond to such changes. Another reason is the ability to share channels on a need to have them basis. However, the best performing prior art dynamic channel assignment systems require some form of intercell communication for each communication request, to coordinate the channel assignments. Disadvantageously, such intercell communication adds latency to the channel assignment process which degrades system performance. Such degradation can be especially acute for high-speed data communication which is bursty and often transfers only small amounts of data at any time, e.g., mouse clicks or packet acknowledgments. Further disadvantageously, the requirement of communication between the base stations places an additional load on the base stations and on the inter-base-stations network, which consumes additional resources and can degrade performance.
We have recognized that, even without intercell coordination on a per communication request basis, channel assignment can be efficiently performed by, developing for each cell, or a sector thereof when the cells are sectorized using directional antennas, a priority list of groups of channels, and selecting a channel to be assigned in response to a request for service from the highest priority group which has available channel at the time of the service request. The priority lists are developed based on various interference measurements that are made. The priority lists tend to remain the same for relatively long periods of time. However, periodically, the priority lists should be redetermined to insure that the best lists are being employed. For example the lists may need to be changed due to new construction or to seasonal vegetation changes, which may affect the interference experienced in the system. Advantageously, system capacity under peak concentrated load conditions may increase. This advantage is further magnified under field conditions for which the cell shapes are not ideal.